1. Field of the Invention
The present invention relates generally to storage area networks. Particularly, the present invention relates to initialization of inter-switch links.
2. Description of the Related Art
Storage networks can comprise several Fibre Channel switches interconnected in a fabric topology. These switches are interconnected by a number of inter-switch links (ISLs), which carry both data and control information. The control path provides connectivity among the switching elements and presents the fabric as a single entity to the end devices. The data paths provide throughput to the end devices connected to the fabric.
For higher throughput, switching elements are often interconnected with parallel redundant ISLs. ISLs terminate at switch ports connected to each switch. These parallel ISLs between a pair of switches can be treated as a single logical interconnection with increased bandwidth. In addition, the increased redundancy can enhance reliability against ISL failures. However, parallel ISLs require multiple resources for the initialization of the associated switch ports. For example, when a fabric is powered on or when a switch is added to an existing fabric, each switch simultaneously begins to bring up all ports. This includes initializing all the ISLs connecting the ports to neighboring fabric switches. Bringing up each port associated with an ISL may involve establishing transmission speed, exchanging link parameters, initialize credit, exchanging lists of switch-to-switch protocols, link resetting, responding to security checks, etc., such that the ports associated with the ISL are activated and ready to proceed to fabric configuration.
Switches may have several ISLs connected between them. For example, the BROCADE® 5300 Switch can support up to 64 ISLs. Performing bringing up or initialization of each port associated with the ISLs requires considerable computing resources in the form of CPU cycle time and memory. Therefore, when a large number of ports are brought up at the same time, the peak resources requirement is very large. However, once the ports have been brought up and the switch has been brought to steady state operation, the need for resources declines considerably (typically by an order of magnitude).
Some efforts have been made to reduce the fabric configuration time once the ports associated with multiple ISLs between two switches have been activated, as discussed in U.S. Patent Application No. US 2006/0168109, entitled “Methods, devices and systems with improved zone merge operation by operating on a switch basis,” which is hereby incorporated by reference. For example, the fabric configuration may involve zone merging on per-switch basis instead of per-port basis. In this case, the zone merge operation is carried out only once per switch pair, and only one ISL per switch pair is involved in the zone merge procedure. However, even the per-switch zone merge method requires that all the ISLs between any two switches be brought up a priori. Therefore it still does not address the problem of high peak resource requirements during port bring up.
Unfortunately, because faster fabric configuration is highly desirable, users are forced to select switching elements that have been designed for peak resource requirements—resulting in increased cost and complexity of the system, while at the same time resulting in underutilized computing resources after the transient peak requirements have receded. Alternatively, if the user decides to select switching elements that are not designed for peak resource requirements, the fabric configuration time increases considerably. In some cases the user is forced to manually initialize each switch one at a time in order to judiciously distribute limited computing resources. But this method requires manual intervention and takes even longer to bring up the network.